1. Field of the Invention
This invention relates to a time indicator, and in particular to a FAIL-SAFE SECURITY ID BADGE which uses a time indicator and which provides a clear indication of expiration of the badge and which acts to prevent unauthorized use of the badge.
2. Related Art
A related time indicator is described in U.S. Pat. No. 4,212,153 to Kydonieus et al. Other related patents include: U.S. Pat. No. 2,337,534 to Barber; U.S. Pat. No. 3,078,182 to Krone, Jr. et al.; U.S. Pat. No. 3,520,124 to Myers; U.S. Pat. No. 3,999,946 to Patel; U.S. Pat. No. 4,643,122 to Seybold; U.S. Pat. No. 4,646,066 to Baughman; U.S. Pat. No. 4,737,463 to Bhattacharjee et al.; and, U.S. Pat. No. 4,903,254 to Haas et al.
U.S. Pat. No. 4,212,153 to Kydonieus et al. describes a laminated time indicator including a two-layer front indicator and a two-layer rear reservoir part. The front indicator part has an indicator layer with an outer display surface and an inner surface having an adhesive layer thereon, e.g., a pressure sensitive adhesive coated onto an opaque barrier layer such as vinyl. The rear reservoir part has a dye or ink film layer and a support card layer.
When assembled, the front part is placed on the rear part with the ink layer forming an assembly joint with the adhesive layer. The dye or ink dissolves in the adhesive. After a period of time the ink migrates from the inner film layer through the adhesive layer and indicator layer to be displayed on the outer surface. In one day, typically, the dye or ink may reach only 20% to 30% of its potential color capacity due to the gradual migration (or absorption) of the dye into the opaque indicator layer and due to the fact that as the concentration of dye increases at the surface, the rate at which the process progresses decreases. Thus, there is no clear indication of when the indicator expired. It is believed that this device has such deficiencies because the opaque indicator layer must be relatively thick to provide mechanical strength to the indicator, creating an extended distance across which the dye or ink must migrate. Also, the opaque indicator layer must have a relatively large quantity of filler, e.g., titanium dioxide, to confer opaqueness to it, and such fillers intermix and absorb with the dye as the dye migrates through the indicator layer, thus diluting or decreasing the intensity of the dye.
U.S. Pat. No. 2,337,534 to Barber, describes a magazine page exposure time indicator including a photosensitive paper sheet mounted on a magazine page, and a developed photographic film sheet having a series of adjacent portions of varying density mounted over the photosensitive paper sheet.
U.S. Pat. No. 3,078,182 to Krone, Jr., describes a heat-sensing, color-changing adhesive tape for a device to be sterilized in a hospital autoclave including an adhesive layer for attachment, a backing web over the adhesive layer and a visible colored layer over the backing web wherein the colored layer comprises a selected pigment disbursed in a resin binder.
U.S. Pat. No. 3,520,124 to Myers, describes a parked car time indicator which includes a first sheet having a first reactant and a second sheet having a second reactant and a release sheet which is peeled away to permit contact of the first sheet with the second sheet to begin a reaction which extends over a selected time interval and terminates with a color change of the reactants.
U.S. Pat. No. 3,999,946 to patel, describes a perishable product time-temperature history indicator which includes a substrate for attachment of the indicator to a product. The indicator shows changes in temperature along a Y-coordinate, over time plotted along the X-coordinate.
U.S. Pat. No. 4,643,122 to Seybold, describes a tamper-indicating security tag which includes a carrier material impregnated with a solution selective compound. The solution is used as a solvent in connection with a sealed enveloping container which controls the rate of diffusion of the solvent.
U.S. Pat. No. 4,646,066 to Baughman, describes an environmental exposure indicator device which includes a target having a tuned circuit and a selective element which receives an interrogation signal in a radio or microwave frequency range, and which also includes an antenna. The antenna receives the signal and the circuit converts the signal to an electrical current. The selective element has an electrical property that changes and responds to the electrical current. The electrical current is dependent upon such environmental factors as temperature, the combination of time and temperature, humidity, radiation, particular fluids and/or mechanical shock.
U.S. Pat. No. 4,737,463 to Bhattacharjee et al., describes a perishable product photoactivitable time-temperature indicator comprising a mixture of a thermally unreactive diacetylenic compound, a photosensitive compound which, on exposure to actinic radiation, forms an acid that converts the diacetylene to a thermally reactive product and an aqueous polymeric medium.
U.S. Pat. No. 4,903,254 to Haas et al., discloses a time indicator comprising: a front portion which includes a transparent layer, an ink display layer, a white barrier layer, an adhesive and ink dissolver layer; and a rear portion which includes a migrating ink pattern layer and a support part. When the time indicator is issued the front portion is placed onto the rear portion and the ink pattern layer is dissolved by the adhesive and ink dissolver layer. The ink pattern then migrates through the adhesive and ink dissolver layer, the white barrier layer, and the ink display layer to the ink display surface layer where it can be visually perceived.